Which database is classified as a document-oriented database?

The classification of a document-oriented database refers to a type of NoSQL database that stores data in the format of documents, typically JSON-like structures. MongoDB is a prime example of this type of database. It is designed to handle large volumes of unstructured or semi-structured data, allowing for a flexible schema and the ability to query data based on its content, rather than a fixed schema as found in traditional relational databases.

MongoDB's strength lies in its ability to store complex data structures through the use of documents, which can encapsulate a variety of data types and structures in a hierarchical manner. This flexibility supports modern application development, particularly in scenarios involving big data, real-time analytics, and applications requiring rapid iteration and deployment.

In contrast, the other options represent different types of databases. Db2 and Db2 Hosted are both traditional relational database management systems (RDBMS), which follow a structured schema and use tables for data storage. Redis is an in-memory key-value store primarily intended for caching and real-time applications, not designed to handle documents as found in document-oriented databases. Thus, MongoDB stands out as the correct choice for a document-oriented database.